Multilayer coating method and apparatus

Abstract

The adhesion of conductive layers to ceramic substrates in the application of such layers by low-energy techniques is improved by interposing between the high-conductivity metal layer and the substrate a layer of refractory metal which is preferably also applied by low-energy vaporization. The metal layers can be provided in succession by reversing the polarity of electrodes composed of the metals of these layers which strike an arc vaporizing the metal to be deposited. One of the electrodes can be shifted out of position and replaced by a substitute electrode and the process repeated to deposit a further layer of metal from the substitute electrode on the substrate.

I claim: 
     
       1. A method of making multilayer metal coatings on a substrate which comprises the steps of: juxtaposing a first electrode of a first metal with a second electrode of a second metal with one another and disposing a substrate in vapor-reversing relationship with said electrodes in a chamber;   evacuating said chamber;   striking an arc between said electrodes in said evacuated chamber while applying one electrical polarity to said first electrode and another electrical polarity to said second electrode to selectively vaporize metal from said first electrode and deposit same upon said substrate;   thereafter reversing the polarities of said electrodes and striking an arc between them to selectively deposit metal from said second electrode on the metal from said first electrode previously deposited upon said substrate; and   thereafter juxtaposing with one of said electrodes a substitute electrode and striking an arc between said substitute electrode and said one of said electrodes in said chamber to vaporize material from said substitute electrode and deposit same on said layer of the metal of said second electrode on said substrate.   
     
     
       2. The method defined in claim 1 wherein said substrate is a ceramic. 
     
     
       3. The method defined in claim 1 wherein said first electrode is composed of a refractory metal. 
     
     
       4. The method defined in claim 3 wherein said refractory metal is selected from the group which consists of tungsten, molybdenum, titanium, zirconium and alloys and combinations thereof. 
     
     
       5. The method defined in claim 1 wherein at least one of said second and substitute electrodes is composed of a metal selected from the group which consists of nickel, copper, gold, silver and alloys thereof. 
     
     
       6. The method defined in claim 1 wherein the layer of the metal of said first electrode is applied in a thickness of the order of microns and the layer formed by one of said second and substitute electrodes has a thickness of 0.01 to 0.02 inches. 
     
     
       7. A method of coating a substrate which comprises the steps of: juxtaposing a pair of electrodes of different metals with a substrate in a chamber;   evacuating said chamber;   applying one electrical polarity to one of said electrodes and the opposite electrical polarity to the other of said electrodes and striking an arc between said electrodes by approximating them into contact and drawings them apart to vaporize material from said one of said electrodes and deposit the vaporized material on said substrate in a first layer while simultaneouly transferring a portion of said material onto the other of said electrodes; and   thereupon reversing the electrical polarity of said electrodes and striking an arc between them to vaporize material from said other electrode including said portion and deposit a mixed layer of materials from both of said electrodes on said first layer as a transition layer and thereafter deposit material from said second electrode onto said transition layer, said other electrode being thereafter shifted out of alignment with said one of said electrodes and being replaced by a substitute electrode with which an arc is struck in said chamber to deposit a further material on said material of said other electrode.   
     
     
       8. An apparatus for multilayer coating of a substrate which comprises: a chamber;   means for evacuating said chamber;   a substrate adapted to be coated being positioned in said chamber;   a pair of first electrodes juxtaposed with one another in said chamber;   means for applying an electrical potential to said electrodes with one of said electrodes having one electrical polarity and the other of said electrodes having the opposite electrical polarity;   means for approximating said electrodes and drawing them apart to strike an arc between said electrodes selectively vaporizing material of said one of said electrodes for deposit upon said substrate in a first layer;   means for reversing the polarities on said electrodes whereby said electrodes strike an arc to deposit material selectively from said other of said electrodes on said first layer; and   means in said chamber for automatically replacing one of the first mentioned electrodes with a substitute electrode and striking an arc between the remaining one of the first mentioned electrodes and said substitute electrode to deposit material of said substitute electrode selectively on said substrate.